The roots of plants grow by a combination of cell divisions and expansion within their tips. These processes are tightly regulated in order to control the amount and direction of root tip growth. To learn more about how this occurs, a novel root waving assay was used to identify an Arabidopsis thaliana mutant named sku5. Root waving, which is a sinusoidal pattern of growth that occurs on a tilted agar surface, is thought to be due to complex root tip responses to gravity, touch, and other environmental stimuli. Instead of waving in downward direction like wild type roots, sku5 roots skew to a horizontal direction as they grow. sku5 roots also grow to be 10 percent shorter than wild type roots and respond to gravity with slower bending kinetics. It was determined that the sku5 mutant phenotype was caused by the T-DNA insertion in a gene encoding a putative pectin esterase- an enzyme thought to be important in regulating cellular expansion by modifying pectin. Pectin is an abundant yet poorly characterized mixture of polysaccharides found in the plant cell wall. Pectin is also an important food source, with wide uses as a gelling agent and soluble fiber, whose properties are commercially enhanced by in vitro treatment with pectin esterases. Computer modeling programs and preliminary data suggest the SKU5 protein gets glycosylphosphatidyl-inositol (GPI) modified- a process which allows for the anchoring of proteins to the plasma membrane. GPI protein anchoring has been found to be essential in animals, yeast, and protozoan pathogens, yet remains uncharacterized in higher plants. Therefore, the study of GPI modification in plants could shed new light on how this process works. The specific aims of this proposed research are to: 1) determine what aspect of cellular growth is affected in sku5 mutant plants; 2) identify the spacial and temporal expression pattern of the SKU5 gene; 3) determine if the SKU5 protein has pectin esterase activity; 4) determine if the SKU5 protein gets GPI modified. The long term goals are to: A) determine how SKU5 is regulated by environmental stimuli; B) identify genes which act in conjunction with SKU5 to regulate cellular growth; C) delineate how and why the SKU5 protein gets GPI modified. This research should add to our understanding of how cell growth is regulated in both plants and animals as well as what mechanisms underly GPI modification.